A river nigger is a Mexican as they use the river to cross over to the USA and jump fences or cross at openings in fences to gain access to the USA. A fence jumper, if you will.
Donald Trump is building a wall to keep the riverniggers outta the states.
An expression used in the card game "Texas Hold 'em Poker" for someone who was losing the hand to one or more players, and was saved by the 5th card, the river, due only to luck, and won the hand.
Bob: "haha, I'm beating you with the odds of 4:1 in favour of me, you only have 3 cards you can hit out of the deck, with one card left, what a crappy call and a horrible read"
Stew: *hits the '3' he needed on the river card*
Bob: "OH MY GOD, HOW LUCKY CAN YOU GET? GO PLAY SLOT MACHINES YOU RIVER NIGGER!"
Ruler of Lake Titicaca. Rumored to have a bunghole that gets very angry if it does not receive toilet paper. Cornholio the Great is often seen walking around with his shirt over his head and his hands in the air, chanting songs about his power, and his bunghole.
"I am Cornholio! You do not want to face the wrath of my bunghole, for I need TP!"
Butthead: Shut up, Beavis! (uh huh huh huh)
Beavis: Um, okay. (heh heh heh heh).